1. Field of the Invention
The present invention relates to a golf ball having a cover, and in particular to a technique for improving abrasion resistance and durability of the cover formed by using a thermoplastic polyurethane as a resin component.
2. Description of the Related Art
As resin components constituting the covers of golf balls, ionomer resins and polyurethanes have been used. Since golf balls having a cover made from an ionomer resin are excellent in repulsion, durability, processability, and the like, they have been widely used. However, problems are pointed out that the golf balls are inferior in shot feeling, insufficient in spin performance, inferior in controllability, and the like due to the high stiffness and hardness of these balls. On the other hand, when polyurethanes are used as the resin component constituting the cover, it is known that the shot feeling and spin property are improved as compared with those of ionomer resins.
For example, Japanese Patent Publication (Laid-Open) No. 2003-515399 discloses, as a golf ball having a polyurethane cover, a golf ball including at least one cover layer, wherein the cover layer is formed from a composition comprising at least one polyurethane containing a hydrophobic backbone, said cover layer having a thickness of from about 0.51 mm (about 0.02 inch) to about 8.89 mm (about 0.35 inch), a hardness of at least about 40 Shore D, a specific gravity of at least about 0.7, a flexural modulus of at least about 3.4 MPa (about 500 psi) and at least about 60 percent dimple coverage, said golf ball having an Atti compression of from about 55 to about 120.
By the way, the polyurethane as the resin component of the cover includes a thermosetting (two-component curable) polyurethane and a thermoplastic polyurethane. In the case of using the thermosetting (two-component curable) polyurethane, a crosslinked structure can be formed and therefore the abrasion resistance of the cover can be improved. However, it is necessary to control the curing reaction during the molding of the cover, and therefore there is a problem that the production process is complicated. On the other hand, in the case of using the thermoplastic polyurethane, since it is possible to mold a cover by directly injecting a cover composition onto a core, the productivity is excellent as compared with that of the thermosetting (two-component curable) polyurethane.